Natural Abundance 13C nuclear magnetic resonance spectroscopy (13C-NMR) will be used to study the structure and dynamics of the binding of various lectins (phytohemagglutinin, wheat germ agglutinin, Vicia graminea anti-N agglutinin), Portuguese man-of-war toxin, and various immunoglobulins to native glycophorin A and N-terminal glycopeptides derived from glycophorin A. This glycoconjugate is the major erythrocyte sialoglycoprotein found in the human erythrocyte membrane. Glycophorin A is also known to contain the receptor for malarial parasites, viruses, and Portuguese man-of-war toxin. Because the receptor sites on glycophorin for the lectins, Portuguese man-of-war toxin, and immunoglobulins, and viruses and malarial parasites are very similar, information gained from these studies will lead to a better understanding of how toxins, viruses, and malarial parasites bind to this glycoconjugate. These studies will be accomplished by monitoring single carbon or individual carbon, protein and carbohydrate resonances of this glycoprotein as a function of added agent (lectins, toxin, immunoglobulins). Difference spectra, pH titration studies, spin-lattice relaxation studies (T1), spin-spin relaxation times (T2), and specific resonance line widths will be used to gain information about the nature of the agent binding site (receptor) on the glycoprotein and the dynamics of the binding phenomena [dissociation constant (K-D), k-off, k-on, delta-H binding, delta-G binding, delta-S Binding, delta-H activation, delta-S activation].